To enlighten this the investigators will conduct a clinical trial concerning complications after RYGB. The investigators will examine 350 RYGB operated patients the Central Denmark Region. From a medical interview, blood tests, Dual energy X-ray absorptiometry etc. it will be possible to give a good estimate of the incidence of medical complications. The investigators will explore complications such as: anemia, hypoglycemia, peripheral nerve problems (especially neuropathies), vitamin D / osteoporosis and other mineral / vitamin deficiencies that may be identified through blood tests. A control group of 30-40 age, sex and body mass index matched individuals will go through the same examinations.